High voltage controls



April 16, 1957 M. B. ARISMAN ETAL HIGH VOLTAGE CONTROLS 5 Sheets-Sheet 1Filed May 20, 1954 imdw pd Mar-mu .5. 44715111211 mlbiri HBudd .Ar'thur' MD 51 April 16, 1957 M. a. ARISMAN ET AL 2,789,191

HIGH VOLTAGE CONTROLS 5 Sheets-Sheet 2 Filed May 20, 1954 M. B. ARISMANETAL HIGH VOLTAGE CONTROLS April 16, 1957 2,789,191

5 Sheets-Sheet 3 Filed May 20, 1954 3W); M ar'vm. .B. Arzsman I V'ZZberbIiBuc? 6 April 15, 1957 M. B. ARISMAN ETAL 2,789,191

HIGH VOLTAGE. commons Filed May 20, 1954 5 Sheets-Sheet 4 Marvin B.Ans-man Wzlbert HBudu" Ari hur Mflaz 2y HIGH VOLTAGE CONTROLS 5Sheets-Sheet 5 Filed May 20, 1954 MarvmfiuAmsman Wilbert H.E u 55 UnitedStates Patent 2,789,191 HIGH VOLTAGE CONTROLS Mervin B. Arisman andWilbert H. Budd, Elkhart, Ind., and Arthur M. Daily, Edwardshurg, Mich.,assignors to Chicago Telephone Supply Corporation, Elkhart, Ind., acorporation of Indiana Application May 20, 1954, Serial No. 431,124 9Claims. (Cl. 201-55) This invention relates to variable resistors of thetype employed in radio and television receivers and has as its purposeto provide a control of this character especially adapted for use withhigh voltages. The advent of socalled color television has created ademand for low cost variable resistors capable of handling voltages onthe order of 15,000 volts above ground and 5,000 volts across the endterminals of the resistor. These voltages are much greater than thosesafely handled by variable resistors now employed in radio and ordinaryblack and white television receivers.

Those skilled in this art will readily appreciate that voltages of thismagnitude create a ditiicult problem in insulation; and this problem isgreatly aggravated if the size of the control is limited. Heretoforedemands for variable resistors capable of handling high voltages weregenerally met without regard for the over-all size of the control.Practically the only factor determining the design of such controls wasthe obtention of adequate insulation to assure against electricalbreakdown. Thus it was common practice in the past to employ arelatively large molded housing and to arrange the resistance element asa curled strip extending along the inside surface of the cylindricalside wall of the housing. This arrangement provided maximum spacebetween the resistance element and the grounded control shaft and alsobetween the resistance element and the collector ring of the centerterminal.

A curled resistance strip, however, does not lend itself to sizereduction. Accordingly, the solution of the problem of providing avariable resistor which is capable of handling high voltages and stillcan satisfy the requirements of set manufacturers for reduction inover-all size compelled abandonment of the curled resistance element andthe substitution of the familiar flat arcuate split ring shapedresistance element which lies flat against the base. Moreover, the flatarcuate element is better suited to production methods of manufactureand hence enables desirable cost reduction. But a flat arcuateresistance element reintroduces the problem of maintaining adequateelectrical spacing between the element and the center collector ring andthe grounded shaft at least if the over-all size of the control is to bekept within the limits prescribed by set manufacturers. The presentinvention solves this problem in an entirely satisfactory manner bymounting and driving the contactor of the control in a novel way.

More specifically this high voltage variable resistor which is sodesigned and constructed that adequate electrical spacing between itsresistance element and collector ring is made possible by a new andnovel otf center disposition of the contactor which allows its collectorring engaging contact fingers or paddles to travel in an orbit closelyadjacent to the axis of the control while its resistance elementengaging contact fingers travel in an orbit spaced a substantialdistance radially out from the axis.

Where the housing of the control is formed in the fainvention provides aso-called miliar way by a cupshaped metal cover joined at its edge tothe base of insulating material upon which the resistance element isfixed, the resistance element should be spaced from the cylindrical sidewall of the cover a distance about as great as its shortest distancefrom the collector ring. This positional relationship utilizes theavailable space to achieve maximum electrical clearance between theresistance element and both the cover and the collector ring, but toattain this desirable condition within a cover of relatively smalldiameter requires that the collector ring be much smaller in diameterthan has heretofore been customary. This in itself, would present noserious difficulty, but when coupled with the desire to use a contactorlike that shown in Patent No. Re. 23,750, and which years of experiencehas proven to be highly satisfactory, a problem was encountered.

The solution of this problem is another object of this invention; and itresides in an extremely eccentric disposition of the contactor so thatits spring contact fingers or paddles which ride upon the collector ringlie at the same side of the axis of rotation as the contact fingers orpaddles which ride upon the resistance element, together with a novelmounting for the contactor assembly by which it is securely held againstany possible rocking and smooth balanced operation of the control isassured.

In instances where the actuating shaft of the control is metal, thisinvention further contemplates an improved driving connection betweenthe shaft and the contactor which not only assures stability for thecontactor, but also maximum insulation between the contactor and thegrounded shaft.

A further object of this invention is to provide a resistor of thecharacter described which is so designed and constructed as to lenditself readily to the incorporation of adequate insulating barriersbetween the portions of the control which operate at maximum potentialdifference.

With the above and other objects in view, which will appear as thedescription proceeds, this invention resides in the novel construction,combination and arrangement of parts substantially as hereinafterdescribed and more particularly defined by the appended claims, it beingunderstood that such changes in the precise embodiment of thehereindiscloscd invention may be made as come within the scope of theclaims.

The accompanying drawings illustrate several complete examples of thephysical embodiments of the invention constructed according to the bestmodes so far devised for the practical application of the principlesthereof, and in which:

Figure l is a longitudinal sectional view through a variable resistorembodying one adaptation of this invention;

Figure 2 is a perspective view illustrating the interior of the housingof the control, the base and contactor assembly being removed therefrom;

Figure 3 is a perspective view of the base and contactor assembly shownseparated, and illustrating the inside aspect of the base with theresistance element and collector ring mounted thereon;

Figure 4 is a perspective view illustrating the inside aspect of a basesuitable for use in the control shown in Figure l, but provided withadditional insulating barriers to be disposed between the resistanceelement and the side wall of the metal housing or cover;

Figure 5 is a cross sectional view through Figure 4 on the plane of line55;

Figure 6 is a longitudinal sectional view through a variable resistorillustrating another adaptation of this invention;

Figure 7 is a perspective view of the inside of the metal cover whichforms part of the housing of that embodiment of the invention shown inFigure 6;

Figure 8 is an exploded perspective view of the other parts of thecontrol shown in Figure 6;

Figure 9 is a longitudinal sectional view through a variable resistorillustrating another embodiment of this invention;

Figure 10 is a perspective view of the base and contactor assembly ofthe resistor shown in Figure 9;

Figure 11 is a perspective view illustrating the interior of the coverof the resistor shown in Figure 9, with the contactor drive arm inposition therein;

Figure 12. is a longitudinal sectional view through a variable resistorillustrating still another modification of this invention;

Figure 13 is a perspective view of the interior of the cover of thatform of the invention shown in Figure 12 and illustrating the oontactorassembly in position therein; and

Figure 14 is a perspective view of the inside aspect of the base of theresistor shown in Figure 12.

Referring now to the accompanying drawings and cspccially to Figures 1,2 and 3, the numeral 5 designates the base of the variable resistorwhich as is customary, is round and may be stamped from. suitable sheetinsulation. A flat arcuate, split-ring shaped resistance element 6 isattached or painted on one side of the base. Where the resistanceelement is a separate piece as shown, it is held in place by terminals 7secured to the base with portions thereof clinched over the ends of theresistance element and other portions projecting through the base toprovide for the attachment of conductor leads thereto.

The base also has a collector ring 8 seated thereon coaxially wifli andinside the arcuate resistance element. The collector ring is held inposition by a center terminal 9 which extends therefrom and passes outthrough the base as shown.

A cup-shaped metal cover 10 preferably formed as a stamping, coacts withthe base to provide a housing for the instrumentalities of the control.The cover has a flat bottom or end wall 11 and a cylindrical side wall12, secured to the peripheral portion of the base in the customarymanner with the end Wall 11 over that side of the base at which theresistance element and collector ring are located. A combined bearingand mounting bushing 13 is fixed to the end wall 11 in coaxialalignment, and journaled in this bushing is a shaft 14 by which therotatable contactor assembly of the control, indicated generally by thenumeral 15, may be driven.

The contactor assembly comprises a stamped and formed contactor 16, ofthe type shown for instance in Patent No. Re. 23,750. The contactor thushas two sets of spring contact fingers or paddles l9 and 20, one totraverse the collector ring and the other to ride upon the resistanceelement, and a pair of cars 18 by which the contactor is fixed to acarrier 17. The carrier is a flat substantially rectangular piece ofstiff insulating material.

The driving connection between the shaft 14 and the contactor assemblycomprises a still arm 21 stamped from sheet metal and fixed to the innerend of the shaft in an elf-center relationship so that one end portionof the arm extends considerably farther from the shaft than the other.The extremities of the arm are bent up to provide a pair of oppositeflat driving lugs 23 flanked by supporting shoulders 24. All of thesupporting shoulders 24 lie in a common plane normal to the shaft axis,and the driving lugs 23 are substantially parallel to one another and tothe shaft axis to fit snugly into slots 25 in the opposite end portionsof the carrier 17.

In order to assure a satisfactory driving connection between the arm 21and the insulated carrier 17 the driving lugs 23 are a bit longer thanthe thickness of the carrier so that when the carrier is seated upon theshoulders 24 the extremities of the lugs protrude slightly above theface of the carrier at which the contactor is located. This brings thedriving lugs, which of course are at ground potential, into closeproximity to the contactor and also the resistance element and collectorring, but an insulating shield 26 of suitably high dielectric strengthaffords the necessary insulation. This shield consists of a piece ofrelatively flexible high dielectric insulating material clamped betweenthe contactor and its carrier with the attaching cars 18 of thecont-actor received in notches in opposite edges of the shield.

The end thrust imposed upon the contactor assembly and the drive arm bythe reaction of the spring contact fingers against the resistanceelement and the collector ring is carried by the inner rolled end 27 ofthe bushing 13 against which the adjacent rear face of the arm 21 bears.A conventional C washer 28 holds the shaft against inward axialdisplacement.

For strength and stillness the arm 21 is preferably channel shaped incross section; and to define the limits of rotation of the contactorassembly the longest end of the arm 21 is shaped to provide oppositeradially disposed edges 29 which coact with stop abutmcnts 30.

The mounting of the control upon a supporting panel (not shown) isaccomplished in the customary manner by a clamping nut threaded on thebushing 13, and to hold the control against turning a log 31 projectsfrom the end Wall 11 of the cover to enact with suitable abutments onthe panel, not shown.

Attention is directed to the fact that the resistance element is spacedradially from the cylindrical side wall 12 of the metal cover or housingunit a distance which is almost as great as the shortest distancebetween the resistance element and the collector ring 8. This positionalrelationship utilizes the space available to achieve maximum electricalspacing between the grounded cover and the resistance element and alsobetween the resistance element and the collector ring, but to gain thisdesired electrical spacing between the resistance element and thecollector ring requires that the collector ring be much smaller indiameter than has heretofore been the practice. To allow such reductionin diameter of the collector ring and still enable the use of thedescribed contactor which experience has shown to be very satisfactory,is one of the accomplishments of this invention.

The unusual extremely eccentric position of the contactor and itscarrier with respect to the shaft and the manner in which the carrier isconnected with the com trol shaft makes it possible to achieve thisdesired result. By this expedient the contact portions of the springfingers or paddles 19 travel in orbits very close to the shaft axiswhile the contact portions of the fingers or paddles 20 travel in orbitsquite a distance out from the shaft axis. In fact, the diameters of theorbit of the paddles 19 are but slightly greater than the diameter ofthe shaft itself, while the orbits of the paddles 20 are outapproximately two-thirds the distance from the shaft axis to the sidewall of the housing.

However, it is not enough that the contactor assc1n bly be arranged inthis off center fashion, for to assure smooth, satisfactory operation,it is also necessary that the mounting of the contactor assembly be suchthat it will be securely held against rocking. This requirement is metby the specific construction of the shaft-carried arm 21 and the mannerin which it is drivingly connected to the carrier 17.

If greater assurance against flash over between the resistance elementand the grounded metal side wall of the housing is necessary it iseasily obtained in the control shown in Figures l, 2 and 3, by theaddition of annular flanges 32 on the inner face of the base as shown,for instance, in Figures 4 and 5. These flanges provide insulatingbarriers lying between the resistance element and the side wall 12 ofthe cover.

In that form of the invention shown in Figures 6 to 8 inclusive, no partof the inside wall of the housing is metal. To this end, the base 5' ofthe control has n cylindrical side wall 35 formed integrally therewith,and a disc 36 of insulating material covers the inside face of the metalend wall 11'. This disc is held in place by being confined between theedge of the side wall 35 and an annular head 37 in the end wall 11'. Themetal cover 10 fits over the molded base unit with its side wall 12'encircling the side wall 35. In keeping with the increased assuranceagainst electrical breakdown afforded by this construction the base hasan insulating barrier 38 formed integrally therewith and lying betweenthe resistance element 6 and the collector ring 8'. Though theresistance element is secured in place by its terminals 7 in the sameway as previously described it should be noted that the element liescloser to the side wall of the housing thus enabling a reduction in thesize of the unit,

In addition, the contactor assembly of this form of the invention isdifferent from that of Figures 1 to 3 inclusive, the chief distinctionbeing in the fact that the carrier 17' and the operating shaft 14' areone integral molding of suitable insulating material. The contactor 16is mounted directly on the carrier, but with this dif ference namely,that both sets of spring fingers or paddles 19 and 20 lie at the sameside of the shaft axis. Hence, the off-center disposition of thecontactor is even greater in this form of the invention than it is inthe construction shown in Figures 1 to 3 inclusive.

Mounting of the collector ring 8 is also somewhat different in that inthis case it rests directly on a central annular boss 41, and therebyobviates the legs by which the collector ring 8 is held at its properelevation.

To provide the necessary smooth running thrust hearing to carry the endthrust imposed upon the rotatable assembly by the spring tension of thecontact fingers the carrier 17' has a hub 39 formed thereon which bearsagainst the adjacent face of the insulating disc 36; and the limits ofrotation of the contactor assembly are defined by a stop lug 40 formedintegrally with the side wall 35 and with which the opposite side edgesof the carrier 17 engage.

The embodiment of the invention shown in Figures 9, 10 and 11, is quitesimilar to that shown in Figures 1, 2 and 3, and differs therefromprincipally in the manner in which the contactor 16 is mounted anddriven. Thus, the contactor, which is identical to the one previouslydescribed and hence like that of Patent No. Re. 23,750, is mounted uponand fixed to a carrier 41 by means of the ears or tabs 18. The carrieris a fiat piece of stiff insulating material shaped as a segment of acircle encompassing an area slightly greater than a semi-circle. Theradius of the arcuate edge of the carrier is but slightly less than theinside diameter of the metal cover 10 so that the carrier provides aneffective insulating barrier between the contactor and the bottom wall11 of the cover and also between the contactor and a metal drivingmember 42 which is fixed to the shaft 14 inside the cover and upon whichthe carrier is mounted.

The driving member 42 is a stiff T-shaped metal stamping fixed to thedrive shaft 14 at the junction of the head and stem of the T, so thatthe driving member provides three arms radiating from the shaft. Theextremeties of the diametrically opposite arms provided by the head orcross bar of the T are formed to have a pair of opposite flat drivinglugs 43 projecting up from adjacent carrier supporting surfaces 44; andthe extremity of the third arm or stem of the T is formed to provide athird carrier supporting surface 45. All of these carrier supportingsurfaces lie in a common plane normal to the shaft axis, and the drivinglugs 43 are substantially parallel to one another and to the shaft axisto fit snugly in diametrically opposite notches 46 in the periphery ofthe insulating carrier 41. Hence the cross bar of the T-shaped drive armis substantially parallel to the straight edge of the carrier and thestem portion of the T extends toward the circular edge of said carrier.

To assure a satisfactory driving connection between the T-shaped drivingmember and the carrier, the driving lugs 43 are slightly longer than thethickness of the carrier so that when the carrier is seated upon itssupports 44 and 45, the extremities of the driving lugs protrude beyondthe face of the carrier at which the contactor is located. However, itshould be noted that because of the size of the carrier, the protrudingends of the driving lugs 43 are spaced a substantial distance from theears or tabs 18 by which the contactor is fixed to the carrier.

The end thrust imposed upon the contactor assembly and the drive arm bythe reaction of the contactor fingers against the resistance element andthe collector ring is carried by the inner rolled end 2'1 of the bearingand mounting bushing 13 against which the adjacent rear face of thedrive arm bears, the drive shaft being held against inward axialdisplacement by the conventional C washer 28 as in the Figure lembodiment of the invention.

To define the limits of rotation of the contactor assembly, the stemportion of the T-shaped driving member is shaped to provide oppositeradially disposed edges 47 which coact with stop abutments 48 shearedand formed inwardly from the end wall 11 of the metal cover. Themounting of the control upon a supporting panel is accomplished in thecustomary manner by a clamping nut threaded onto the bushing 13, and tohold the control against rotational displacement after mounting, a lug49 may be sheared and formed outwardly from the end wall of the metalcover to coact with suitable abutments on the panel.

It will be noted that as in the Figure 1 construction the resistanceelement 6 is spaced from the cylindrical side wall 12 of the metal covera distance which is almost as great as the shortest distance between theresistance element and the collector ring 8. This positionalrelationship again utilizes the space available to achieve maximumelectrical clearance between the cover and the resistance element, andalso between the resistance element and the collector ring, which asexplained before, is much smaller in diameter than has heretofore beencustomary. To accommodate this reduction in diameter of the collectorring and still use the previously described highly satisfactorycontactor, the contactor has been placed in an extremely eccentricposition with respect to the drive shaft so that both sets of its springcontact fingers 19 and 20 lie at the same side of the shaft axis withtheir extremities encompassed by an area which lies inside of and issubstantially equispaced from the three supports 44 and 45 upon whichthe carrier rests. This three point support for the contact carrier thuscarries the thrust of the contact fingers in a manner which assuresagainst rocking of the contactor and achieves well balanced smoothoperation for the control.

In the embodiment of the invention shown in Figures l2, l3 and 14, theshaft 14' and the contactor drive arm 17' are parts of a unitary moldingof suitable insulating material as in that form of the invention shownin Figures 6, 7 and 8, and the contactor 16 is secured to the drive arm17' by having its ears or tabs 18 received in notches in the sides ofthe arm and clinched thereover. Both sets of spring contact fingers lieat the same side of the shaft axis in position to traverse theresistance element and the collector ring, and the end thrust imposedupon the contactor assembly by the spring contact fingers is carried tothe end wall 11 of the cover by a relatively small diameter hub 39 onthe back of the drive arm 17'.

Assurance against rocking of the contactor assembly is obtained in thisconstruction through the use of two side thrust bearings 50 and 51. Thebearing 50 is extruded from the back wall 11 of the cover and receivesthe shaft 14, while the bearing 51 is a hole in the base 5 whichreceives a trunnion 52 formed as an integral part of the arm 17coaxially with the shaft. Obviously, of course, the bearings 50 and 51must be exactly coaxial.

The limits of rotation of the contactor assembly are defined by a stop53 struck in from the end wall 11 in position to be engaged by the sideedge portions 54 of the driving member 17'; and outwardly struck ears ortabs 55 project from the front face of the wall 11 to provide means formounting the resistor upon a panel.

From the foregoing description taken in connection with the accompanyingdrawings it will be readily apparent to those skilled in this art thatthis invention provides a variable resistor which not only is capable ofhandling exceptionally high voltages, but by virtue of its novel designand construction achieves an entirely un precedented reduction in sizefor controls of this type and enables the control to be made withrelatively inex pensive production methods.

What We claim as our invention is:

l. In a variable resistor having a base of insulating material, a flatarcuatc resistance element on one side of the base, a collector ring onthe same side of the base concentrically surrounded by the arcuateresistance element, and a contactor having spring contact fingers totraverse the resistance element and the collector ring. means formounting and driving the contactor, comprising: a shaft constrained torotation about an axis perpendicuiar to the base and concentric to theresistance element and the collector ring; a driving member fixed to theshaft and having arms radiating therefrom; supporting surfaces on theouter ends of said arms facing the base and lying in a plane normal tothe shaft axis; an insulated contactor carrier seated near its peripheryon said supporting surfaces; torque transmitting driving lugs on thedriving member engaging in openings in the contact carrier; and meanssecuring the contactor to the side of its carrier which faces the basewith its contact fingers in position to traverse the resistance elementand the collector ring and with the extremities of all of its contactfingers lying closer to the shaft axis than do said supporting surfaceson the driving member.

2. In a variable resistor, the structure set forth in claim 1 furthercharacterized by the fact that the securement of the contactor to itscarrier so disposes the same thereon that the extremities of all of itsspring contact fingers lie at the same side of the shaft axis.

3. In a variable resistor, the structure set forth in claim 1 furthercharacterized by the fact that the driving member is a stiff T-sha'pedmetal stamping having two diametrically opposite arms and a third armsubstantially at right angles to said diametrically opposite arms;supporting surfaces on the extremities of said three arms substantiallyspaced from the shaft axis, facing the base and lying in a plane normalto the shaft axis to provide a three point support for the contactorcarrier; and further characterized by the fact that the extremities ofthe spring contact fingers lie in an area disposed within andsubstantially spaced from said three supporting surfaces.

4. in a variable resistor. the structure set forth in claim 3 furthercharacterized by the fact that said torque transmitting driving lugs areon the extremities of the diametrically opposite arms of the drivemember; and that the openings in the contactor carrier in which saidlugs are received are notches in the peripheral edge portion of thecarrier.

5. A variable resistor of the type wherein a stator assembly and a rotorassembly are contained Within a housing having opposite end walls, thestator assembly comprising a flat arcuate resistance element andconcentrically therewith, a center terminal collector ring, both on oneof the end walls of the housing. and the rotor assembly including anoperating shaft journaled in a bearing in the other end Wall of thehousing concentrically with the resistance element, characterized by thefact that the rotor assembly further comprises a contactor carrier ofinsulating material; a metal driving member fixed to the shaft andhaving arms extending therefrom in a plane normal to the shaft;supporting surfaces on the outer ends of the arms facing the statorassembly til) and bearing against the contact carrier; torquetransmitting driving lugs on the metal driving member engaging inopenings in the contact carrier; and a bridging contactor affixed to thecontactor carrier, said bridging contacror having spring fingers withcontact pads on the outer ends thereof positioned to traverse theresistance element and the collector ring, all of the spring contactfingers lying closer to the axis of the operating shaft than to saidsupporting surfaces and torque transmitting driving lugs so as to assuregood electrical clearance between the contact lingers and the drivinglugs.

6. A variable resistor especially adapted for use with high voltagecomprising: a base of insulating material; a fiat ar-cuate resistanceelement on one side of the base; a flat center terminal connector ringon said side of the base inside and concentric with the arcuateresistance element but spaced therefrom a distance suflicient to preventilashover between the resistance eiernent and collector ring at thevoltages for which the resistor is de signed; a housing for theinstrumentalities of the variable resistor, said housing comprising thebase and a stamped metal cover inverted over and secured to the basewith its end wall overlying the side of the base at which the resistanceelement and collector ring are located; an operating shaft for theresistor journallcd in a bearing carried by the end wall of the metalcover and concentrically disposed with respect to the areuate resistanceelement and the collector ring; and a rotatable contactor assemblyWithin the housing driven by said shaft and comprising an insulatedcontact carrier consisting of a flat piece of insulating material, acontactor fixed to said piece of insulating material and having a springcontact finger to ride upon the resistance element and another springcontact finger to ride upon the collector ring, and means connectingsaid piece of insulating material to the shaft comprising a metal armfixed to the shaft and projecting radially in opposite directionstherefrom, torque transmitting driving lugs extending from the oppositeends of the arm parallel to the shaft axis and toward the base,supporting shoulders on said arm flanking each of said torquetransmitting driving lugs and facing the base, all of said supportingshoulders lying in a common plane normal to the shaft axis, said torquetransmitting driving lugs being readily removably received in closefitting openings in the flat piece of insulating material and thereby sopositioning the contact carrier with respect to the shaft, that itsspring contact fingers are correctly aligned with the resistance elementand collector ring, the reaction of the spring fingers against theresistance element and collector ring holding the piece of insulatingmaterial against the supporting shoulders to thereby establish andmaintain a predetermined contact pressure.

7. The variable resistor of claim 6 further characterized by the factthat the contact portions of both of said spring fingers of thecontractor are disposed at the same side of the shaft axis.

8. The variable resistor of claim 6 further characterized by the factthat the contact carrier comprises a substantially rectangular flatpiece of insulating material having slots in its end portions, thecontactor being a sheet metal stamping and being secured to thesubstantially rectangular piece of insulating material and overlying oneside thereof, an insulating shield interposed between the contactor andthe piece of insulating material and substantially covering the entirearea of the latter so as to overlie the slots in its opposite endportions; and further characterized by the fact that the connectionbetween the shaft and the carrier comprises a stamped metal arm fixed tothe shaft and having opposite end portions extending in oppositedirections from the shaft axis, one of said arms being substantiallylonger than the other, the extremities of the arm being bent up toprovide driving lugs flanked by supporting shoulders all of which lie ina common plane normal to'the shaft axis, the

driving lugs being received in the slots in the piece of axial positionof the shaft and the contactor driving meminsulating material; thereaction of the spring fingers bet with respect to the base; and meansmounting the against the resistance element and collector ring holdingcontactor on said driving member at said side thereof the piece ofinsulating material against the supporting which faces the base and withthe spring contact fingers of shoulders, and the insulating shieldproviding insulation 5 the contactor in position to traverse theresistance elebetween the driving lugs and the contactor. ment and thecollector ring, said contactor mounting 9. In a variable resistor havinga base of insulating means so locating the contactor on the drivingmember material, a fiat arcuate resistance element on one side of thatthe extremities of all of its spring contact fingers the base, acollector ring on the same side of the base lie at the same side of theshaft axis.

concentrically surrounded by the arcuate resistance ele l0 merit, and acontactor having spring contact fingers to References Cited in the fileof this P traverse the resistance element and the collector ring, UNiTEDS A PATENTS means for mountlngand driving the contactor, compris-2,176,090 McAU-lster et aL Oct 17 1939 mg. a shaft constrained torotatlon about an axis per- 2628 298 Budd Feb 10 1953 pendicular to thebase and with which axis the resistance 15 u element and collector ringare concentric; a contactor R N PATENTS driving member fixed to theshaft and radiating there- 3 3 9 Great Britain 2 1 5 from with one sideof the driving member facing and overlying the base; thrust bearingmeans defining the

